1. Field of the Invention
The present invention relates to a backlight unit including a heat dissipating layer. Particularly, the present invention relates to a backlight unit including a heat dissipating layer capable of improving temperature characteristics of a display device, a display device including a heat dissipating layer, and a method for manufacturing a heat dissipating layer.
2. Description of the Related Art
A Liquid Crystal Display device (LCD device) is an electrical device which changes electrical data into visual data, and displays them by varying the liquid crystal transmisstance according to an applied voltage.
The LCD device is a device for displaying information, but cannot emitting the light by itself. Thus, the LCD device needs an extra device as a light source to uniformly brighten the entire screen from the rear surface of the LCD device. A Back Light Unit (BLU) is used to provide a light to the screen of the LCD device.
The BLU is classified into a direct-light type and an edge-light type according to the installed position of a light source. In the direct-light type BLU, the light source is disposed under a liquid crystal panel, and in the edge-light type BLU, the light source is disposed on a lateral side of a light guiding plate.
The edge-light type BLU comprises a light source unit, a light guiding plate, a reflector, and an optical film. The light source unit comprises at least one light source generating a light with a predetermined wavelength, and a light source reflector. The light generated from the light source is reflected by the light source reflector made of reflective material, and the reflector. Then, the reflected light is diffused uniformly through the entire light guiding plate. The optical film comprises a diffuser, a prism sheet, and a protection sheet.
The function of each element in the optical film is explained as follows. The light uniformly diffused in the light guiding plate passes through the diffuser. The diffuser diffuses or condenses the light passing through the light guiding plate so that the brightness becomes uniform and the viewing angle becomes wider.
The brightness of the light passing through the diffuser is remarkably decreased. To solve this problem, a prism sheet is used. The prism sheet refracts the light passing through the diffuser, and converges the light incident in a low angle to the direction substantially perpendicular to the prism sheet so that the brightness is increased within the range of the effective viewing angle. The protection sheet is disposed on the prism sheet. to prevent the prism sheet from being damaged, and makes the narrowed viewing angle wider.
A Cold Cathode Fluorescent Lamp (CCFL) is used mainly as the light source of the BLU. As the BLU installed to a liquid crystal panel emits the light, the inside temperature of the LCD device is increased, and the temperature of the CCFL is increased up to 80° C. to 90° C. Thus, the efficiency of the BLU is lowed, and the brightness of the LCD device is decreased.
Unlike the edge-light type BLU, the direct-light type BLU has a reflector under the light source. In this structure, most heat generated from the light source is transferred to the reflector. The reflector is overheated by the transferred heat, and thus may be deformed.
In addition, although it may be different according to the type of BLU, most heat generated from the CCFL is transferred to the liquid crystal panel disposed on the front surface of the BLU. Therefore, a temperature difference among the liquid crystal cells may occur. Such a temperature difference among the liquid crystal cells causes the response speed difference among the liquid crystal cells, which causes the brightness difference of the LCD device.
A Plasma Display Panel (PDP) is a light-emitting display device having a plurality of discharge cells disposed between a pair of glass substrate. Unlike the LCD device, the PDP does not need an extra light source. However, in the PDP, the discharge cell that is activated to emit a light for displaying an image generates heat. Therefore, the temperature of the PDP is increased. That is, the heat generated in the discharge cell is transferred to a glass substrate, but is not transferred in a parallel direction to a panel surface due to the low thermal conductivity of the glass material having.
In addition, the temperature of the activated discharge cell is increased remarkably, but the temperature of the non-activated discharge cell is not increased as much as the activated discharge cell. Thus, the temperature of the panel is increased non-uniformly in an image-forming area. This temperature difference affect the lifetime of the discharge cells.
Besides the LCD device or PDP described above, such a problem occurs in a display device using an light emitting diode or organic electroluminescent device, affect the durability or the display quality of the device.
Thus, there has been a need to provide a solution that can transfer the heat generated in the device to the outside effectively.